December 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
conversion is increased and as the reactor temperature is decreased. At similar processing conditions the sulfur content is very nearly the same in w o l i n e s produced by the use of silica-alumina, silicamagnesia, or Filtrol catalysts. In most cases the concentration of sulfur in a cracked gasoline is approximately 10% of that in the feed stock a t 60% conversion and 900" F., although gasolines produced from certain California feeds contain greater amounts of sulfur, while gasolines from a very few feeds contain lesser concentrations of sulfur. The F-2 octane number response to the addition of tetraethyllead to catdytic gasolines has been related to their content of sulfur and olefin, both of which are detrimental to lead response.
ACKNOWLEDGMENT
2687
and Automotive and Aircraft Laboratory of Universal Oil Products Company, Riverside, 111. Acknowledgment is due K. M. Brown of Universal Oil Products Company for helpful suggestions used in preparing this paper.
LITERATURE CITED Eastman, DuBois, IND. ENG.CHEM.,33,1555 (1941). (2) Fowle, M.J., and Bent, R. D., Oil Gas J., 46, No.27,209 (1947). ENQ.CnEM., 31,850 (1939). (3) Graves, F. G., IND. ENG.CHEM., ANAL.ED., (4) Grosse, A. V., and Wackher, R. C., IND. 11,614(1939). ENG.CEEM,, (5) Hebl, L. E., Rendel, T. B., and Garton, F. L., IND. 31,862(1939). (6) Livingston, H. K., Oil Gas J.,46,No.45, 80 (1948). IND. ENG.CHEM.,34,824 (1942). (7) Ryan, J. G., (8) Trusty, A. W.,Refiner Natural Gasoline M f r . , 19, No. 4, 53 (1940).
A large mrtion of the reported experimental data was obtained v
-
by members of the Pilot Piant Division, Analytical Laboratories,
R
~.4p,r,l8 , ~1949.
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1
Sulfur Distribution in Thermal Cracking of High-Sulfur Feed Stocks J. M. BARRON, A. R. V A N D E R P L O E G , AND HUBERT M C R E Y N O L D S The Texas Company, Port Arthur, Tex. Sulfur in charge and in gasoline is shown for thermal cracking several stocks from California, West Texas, Wyoming, Venezuelan, Mexican, and Arabian crudes. A simple factor is proposed for predicting the sulfur content of thermally cracked gasoline from the sulfur content of the charge for each of the above crude sources. Sulfur distribution between gas, gasoline, and bottoms from thermal cracking is shown for stocks from West Texas, Wyoming, and Arabian crude sources. Effect of conversion level on sulfur distribution is shown for thermal cracking of Arabian gas oil.
T
HERE hras been an increasing interest in the sulfur contents
11
of petroleum fractions paralleling the increase in high-sulfur crude processing in the petroleum industry. This interest is primarily in the refined oils which are blended into the marketed product. The different components which may be employed in a finished gasoline frequently require different processing methods. The removal of sulfur from straight-run gasolines can be done relatively inexpensively by several methods. The removal of sulfur from cracked gasolines is a much more expensive operation, with the exception of mercaptan (thiol) removal which usually represents a small part of the total sulfur in a stabilized gasoline. I n many cases it is desirable to use low-sulfur straight-run gasolines, or high-sulfur straight-run gasolines after sulfur removal, as blending stocks with high-sulfur cracked gasolines to produce a marketable product. It is essential to know the sulfur content of cracked gasolines and the first purpose of this paper is to show the sulfur content of cracked gasoline from thermal cracking operations on stocks from several crude sources. The thermal processing of stocks derived from high-sulfur crudes also requires a knowledge of the sulfur distribution between the products from the thermal cracking operation. It is
the second purpose of this paper to show the sulfur distribution in the products from thermal cracking operations on stocks from three crude sources. In general, the term gasoline as used throughout this paper refers to a 400 o F.-end point distillate (A.S.T.M. method D 86-40) stabilized to roughly a %pound Reid vapor pressure (A.S.T.M, Method D 323-43).
SULFUR CONTENT OF THERMALLY CRACKED GASOLINES Recently, ill. J. Fowle and R. D. Bent published a paper (6) showing the sulfur distribution for several types of petroleum processing. This work was based on processing mixtures of West Texas crudes. From their work it appeared that the sulfur content of the distillate from thermal cracking was a constant percentage of the sulfur content of the feed to the thermal cracking operation. In order to extend this picture, the above principle was applied to thermal cracking operations on gas oils and residual oils from the six high sulfur crude sources shown in Table I. These data, plotted in Figure 1, indicate a wide spread in the factors (ratio of sulfur in gasoline to sulfur in charge) from a value of 0.06 for Arabian crude stocks to 0.44 for California stocks, which is a difference of slightly over seven times. As shown in Figure 1, i t appears possible to segregate the data by crude source. Although there ie some scatter in the data, i t appears valid to average the factors for each crude source as indicated below: % ' S in Gasoline Crude Source California West Texas Wyoming
Venezuelan Mexican Arabian
% €3 in Charge 0.34 0.18 0.16 0.13
0.10
0.0s
2688
INDUSTRIAL AND ENGINEERING CHEMISTRY
operations are presented in Table I11 and yields and product quality data are presented in Table 1V. The Wyoming stocks also contained the residual fractions and were processed in a similar operation to both fuel and coke in the plant and to coke only in the laboratory. The sulfur balance data from these operations are presented in Table V and yields and product quality data are presented in Table VI. The heavy Arabian gas oil was procebsed in a single-pass operation in a series of runs during which the conversion was varied from 11.5to 31.1 weight % gas oil disappearance. The sulfur balance data from these operations are presented in Table VII. The sulfur recovery was good in the single-pass cracking operation but was generally poor in the recycle operation. There is no
W'
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g 0.4 < (3
z 4
Vol. 41, No. 12
0.2
LL
-I
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0.0
SULFUR IN CHARGE, WT. %
Figure 1, Variation of S u l f u r i n Cracked Gasoline w i t h S u l f u r in Charge
I.*
r
These data indicate that u hen thermally cracking stocks of the same sulfur content, the California cracked gasoline mill have a sulfur content roughly four times greater than the Arabian 2.6 cracked gasoline. The West Texas and Wyoming cracked gasolines mill be roughly tv&e as high in sulfur as the Arabian cracked gasoline, while the Venezuelan and Mexican cracked gasoline8 are only slightly higher in sulfur content than the Arabian. This sulfur factor appears to be relatively insensitive to the type operation employed. The vr-ide range in types of operation, shoan in Table I, include gas oil, topped crude, and residuum cracking in both single-pass and recycle operations to coke and to fuel. Although these differences in operation probably have some effect, it is indicated to be relatively small in comparison to the CONVERSION, 100 - WT. W BOTTOMS effect of crude source. A factor of 0.23 was calculated from the above-mentioned data Figure 2. Variation of S u l f u r C o n t e n t in P r o d u c t s w i t h Conversion of Foale and Bent for West Texas crude stocks as compared to 0.18 shown by the data presented here. This difference is not large, considering that there are probably variables other Table 1. S u l f u r C o n t e n t of Gasoline from T h e r m a l Cracking Operations than the type operation which have an effect, such as diffcrences in the various Crude Source pools or production levcls that occur S i n Gasoline of Charge Bomb ~ ~by ~ % d , within a given crude classification. The Stock Method L a m p Method 70 9 i n Charge Type Operation fact that it appears possible t o segregate West Texas crudes 1.64 0.31 0.20 Recycle cracking t o fuel Plant the data according to this rather rough 1.67 0.29 0.18 Recycle cracking t o fuel Plant 1.67 0.25 0.15 Recycle cracking t o furl Laboratory classification of crude source is of con2.75 0.50 0.18 Recycle cracking t o fuel Laboratory siderable interest and probably indicates 0 .18 A\.. Wyoming crudes that the sulfur is associated with similar 0 14 Recycle cracking t o fuel and coke 0.23 1.69 Planta 0.25 Recycle cracking to coke 0.13 hydrocarbon types in each crude source. 0.53 Laboratory
1
SULFUR DISTRIBUTION PROM THERMAL CRACKING The factors developed above can bc used only for estimating the sulfur content of the cracked gasoline. It would be desirable to be able t o estimate the sulfur content of the gas and bottom fractions as well, but sufficient data for this purpose are not available. CompIete sulfur balances are available for coventional plant and laboratory thermal cracking operations on stocks from three of these crude sources (West Texas, Wyoming, and Arabian). Tests on the charge stocks are presented in Table 11. The West Texas stocks containing the residual fractions of the crude were processed in both laboratory and plant two-recycle stream operations tu fuel. The sulfur balance data from these
Laboratory Laboratory" Laboratory
2.80 2.46 3.53
0.32 0.33 0.70
0.12 0 13 0.20 0 . 1 6 Av.
Recycle cracking t o coke Recycle cracking to coke Recycle cracking t o coke
California crudes Plant Laboratory Laboratory Laborat,ory
1.26 1.56 1.06
0.55
0.44 0.34 0.27 0.29 0 . 3 4 dr.
Recycle cracking to fuel Recycle cracking t o fuel Recycle cracking t o fuelb Single-pass coking
3.04 3.04
0.18 0.27 0.50 0.12
0.06
Recycle cracking to fuel Recycle cracking t o fuel cokea n d pitch
Arabian crudes Plant Plant Laboratory Laborators Venezuelan crudes Plant Plant Laboratory (2) Laboratory (4) Laboratory (8) Laboratory (3) Mexican crudes Laboratory 4) Laboratory i4) Laboratory (4) Laboratory (4) Laboratory (4) a
b
2.5i
4.78 1.77
0.53 0.29 0.75
0.09 0.10 0.07 0 . 08 Av.
Single-pass gas oil cracking
2.45
0.36 0.12 0.25 0.26 0.13 0.14
0.14 0.11 0.15 0.15 0.08 0.12 0 . 1 3 Av.
Recvcle RecGcle Recycle Recycle Recycle Recycle
1.22
0.13 0.19 0.19 0 21
0.11 0.08
Recvcle RecGcle cracking to fuel
1.06 1.65 1.72 1.57 1.16
2.46
2.36 2.05 1.98
0.22
Contained catalytic cycle gas oil. Charging gas oil from single-pass coking.
0.08
0.10 0.11 0 . 10 AI,.
cracking cracking cracking cracking cracking cracking
t o fuel
to to to to to
fuel fuel fuel fuel fuel
Recycle cracking t o fuel Recycle cracking t o fuel Recycle cracking t o fuel
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
December 1949
2689
Table 11. Tests on Charge Stocks Operation
T o fuel
T o fuel
T o fuel a n d coke
T o coke
T o coke
Single-pass cracking
Description of charge
West Texas reduced crude with 34% thermal cycle gas oil
West Texas topped crude
Wyoming residuum with 71 % cat. cycle gas oil
Wyoming reduced crude
Wyoming residuum with42% cat. cycle gas oil
Arabian gas oil
21.3 1.59
17.8 2.80
15.3 2.46
29.3 1.77
571 058
610 663 746
Gravity OA.P.1. Sulfur (bomb), wt. % A.S.T.M. distillation, 10% recovered 50% recovered 90% recovered
25.4 1.67
18.3 2.75
F.
466 676
516 721
....
....
468 592
596 738
....
....
....
~~
Table 111. Sulfur Data on West Texas Crude Fractions West Texas Topped Crude Plant R u n 7 Sulfur, Yield, Sulfur, wt. % wt. % wt. % charge charge component sulfur Factora Gasoline Fuel oil Gas Recovery Gasoline mercaptan a
46.5 42.2 11.3 100.0
...
0.292 2.36 2.63
...
0.10
8.1 59.0 17.8 85.5
..
--
0.18 1.41 1.57
40.1 46.6 13.3 100.0
..
. .
5.8 65.8 14.4 80.0
0.241 2.36 1 .81
0.14 1.41 1.08
..
...
..
..
01075
22.2 64.0 13.8 100.0
0.50 3.21 2.78 0 : io
4.0 74.7 14.0 92.7
0.18
1.17 1.01
.. ..
, .
Ratio of sulfur content in component to sulfur in charge.
apparent explanation of this discrepancy since considerable care was exercised in attempting to obtain complete sulfur recoveries. In the course of the laboratory work on Wyoming stocks, an attempt was made to improve sulfur recovery by "sulfiding" the laboratory unit. Two methods of sulfiding were employed. Repeated running on a high sulfur stock before charging the experimental stock, employing stainless steel coke drums, and maintaining a n inert gas (neuhral flue gas) in the unit when not in operation. Purging and pressuring the unit with hydrogen sulfide before starting a run. Neither operation resulted in any appreciable improvement in sulfur recovery and it was concluded that hydrogen sulfide corrosion of the unit was not a serious factor in causing low weight recoveries. The sulfur analyses were made by conventional methods; sulfur content of the charge stock was determined by the bomb method (A.S.T.M. Method D129-44); of the gasoline, by the lamp method (A.S.T.M. Method D 90-47T); and of the gas by the Tutwieler ( 1 ) method. Although it is realized that a slightly higher sulfur recovery might have been obtained if the gasoline
Table V.
Gasoline ' Fuel oil Coke Gas Recovery Gasoline merca t a n sulfur, wt.
3
Table IV. Yields and Product Inspections from Thermal Cracking West Texas Crude Fractions West Texaa Topped Crude, West Texas Topped Crude, Laboratory Run Plant Run Yields, wt. % Gasoline Fuel oil Gas Total
40.5 42.2 11.3 100.0
40.1 46.6 13.3 100.0
-
-
58.9 0.292 0.100 10.0
56.1 0.241 0.075 9.6
55.1 0.500 0.100 4.3
94 126 248 372 404
103 146 242 340 388
235
~
Product inspection Gasoline, stabilized Gravity, A.P.I. Sulfur, wt. % Mercaptans, wt. ?& Reid vapor pressure A.S.T.M. distillation, O F. Initial boiling point 10%
50%
$9
point
West Texas Reduced Crude with 34% Thermal Cycle Gas Oil, Laboratory R u n 22.2 64.0 13.8 100.0
123 159 344 392
Fuel oil Gravity O A.P.I. Viscosit;, Saybolt Furol a t 122O E'. Sulfur, wt. %
4.6
6.8
6.6
109 2.36
104 2.36
3.21
Gas Molecular weight Sulfur, wt. %
29.1 2.63
33.2 1.81
33.8 2.78
70
Sulfur Data from Wyoming Crude Fractions
Wyoming Residuum with 71% Catalytic Cycle Gas Oil 7 Plant R u n Sulfur, Yield, Sulfur, wt. 7' wt. % wt. % charge charge component sulfur Factora
Q
West Texas Reduced Crude with 34% Thermal Cycle Gas Oil Laboratory RunSulfur, Yield, Sulfur, wt. % wt. % wt. % charge charge component sulfur Factor"
West Texas Topped Crude Laboratory R u n Sulfur, Yield, Sulfur, wt. % wt. % wt. % charge charge component sulfur Factora
32.6 28.0 21.0 18.4 100.0
0.23 2.82 1.88 1.34
..
4.7 51.4 24.8 15.5 96.4
0.14 1.77 1.18 0.84
...
0.055
..
Wyoming Reduced Crude Laboratory Ru-7 Sulfur, Yield, Sulfur, wt. % wt. % wt. % charge charge component sulfur Factora
c
50.2
5.8
0.12
46.1
..
31.2 18.6 100.0
3.81 4.6
...
4i:4 30.6 78.8
1:36 1.64
..
34.9 19.0 100.0
3.49 3.52
..
...
0.056
..
..
...
0.061
Ratio of sulfur content in component to sulfur content of charge.
....
0.323
Wyoming Residuum with 42y0 Catalytic Cycle Gas Oil Laboratory R u n Sulfur Yield, Sulfur, wt. % wt. % wt. % charge charge component sulfur Factor"
...
...
0.33
...
...
6.2
0.13
4i:5 27.2 82.9
1:42 1.43
.
I
.. ..
INDUSTRIAL AND ENGINEERING CHEMISTRY
2690
Vol. 41, No. 12
bottoms was greater than in the charge stock. The major portion of the sulfur originally present in the charge is contained in t'his fraction. The gas also contains an appreciable quantity of Wyoming Wyoming Wyoming Residuum sulfur and the sulfur concentration was even higher than i n the Residuum with Reduced ~ ~ bottoms 1 fraction in ~ some instances. ~ This sulfur ~ in the 1gas is pri- ~ & \ ~ L ~Laf~,u,dted,y ~ ~ l ~ ~ { Plant R u n Run Laboratory R u n marily. hydrogen sulfide since only minute quantities of mercauYields, yt. % 32.6 50.2 46.1 'tan are normally prescnt. The gasoline fraction contains only a Gasoline 28.0 ... Fuel Oil small quantity of sulfur relative to the feed. 21.0 31.2 34.9 Coke Gas 18.4 ___ 18.6 19.0 The effect of conversion on sulfur distribution for an Arabian 100.0 100 I O 100.0 Total gas oil is shown in Figure 2, which is a plot of the data presented Product inspection in Table VII. It appears that the sulfur content of the gasoline Gasoline, stabilized 57.2 54.9 55.9 Gravity, ' A.P.I. fraction is essentially unaffected by conversion except a t low con0.330 0.226 0.323 Sulfur a t . % Merckptans, wt. % 0 055 0.056 0.061 version levels. In this range it appears that the sulfur content of 4.5 11.1 5.8 Reid vapor pressure the gasoline increases slightly. The sulfur content of the bottoms A.S.T.M. distillation, F. increases with conversion whereas t,he sulfur content of the gas Initial boiling point 107 92 I09 decreases. 141 128 148 10% 236 267 257 Since conversion affects t,he sulfur concentration in the gas and 351 388 351 bottoms fraction, the sulfur concentrations in these fractions can386 406 417 E n d point not be estimated by multiplying the sulfur content of the charge Fuel 011 7.1 . , ~ , . . Gravity, A.P.I. by a simple factor such as was developed for gasolines in Figure 1. Viscosity Saybolt 63 ... The relatively wide scatter of the factors for gas and bottoms preUnivcr'sal a t 1220 F 2.82 ... Sulfur, wt. % sented in Tables 111 and V confirms this conclusion. It is interGas esting to note, however, that 14.0 t'o 17.8 weight % of the sulfur 32.5 25.4 ?7.0 Molecular weight 1.31 4.60 *+. 5 2 Sulfur, wt. % present in the charge was accounted for in the gas fraction from coke recycle operations to fuel on West Texas stocks. This increased Volatile and combus../ 9.6 tible matter, wt. % t o 27.2 to 30.6 weight % charge sulfur in the gas for recycle opera10.3 . ~ . None None Moisture. wt. '3 ... 0.23 0.37 tions to coke on Wyoming stocks. When processing the Wyoming Ash wt. '% Buliur, wt. % 1.88 3.81. 3.49 stock to both fuel and coke only 15 m i g h t % of the charge sulfur was in the gas fraction. This may indicate an Table VII. S u l f u r Data from Single-PassCracking of Arabian Gas Oil effect of the type operation on the Sulfur, W t . o/c Charge Sulfur Yields, Wt. 70 Sulfur Content, Wt. Run NaphBotNaphBotNaphBotamount of sulfur appearing in the gas. No. tha toms Gas tha toms Gas tha toms Gas Total The effect of conversion on this value, P 9.6 86.8 3.8 0.138 1.91 1.7 0.7 93.7 3.7 98.1 as shown by the data in Table VI1 12.2 85.3 2.5 0.116 2.00 0.8 96.3 .. 2 is not clear owing to the scatter of the 3 13.5 83.9 2.6 0.119 2.02 i.3 0.9 96.7 1.9 9815 4 15.5 81.0 3.5 0.108 2.12 10 97.0 data, but there does seem to be some in5" 24.7 88.9 6.4 0.113 2.28 i.'l 116 88.8 4.b 9414 crease with conversion up to a maximum 60 24.0 69.4 6.6 0.125 2.33 1.1 1.7 91.3 4.1 97.: 7 9.5 88.5 2.0 0.148 1.90 1.5 0.8 95.0 1.7 87.3 of about 4 weight yo charge sulfur in the 1 7 . 8 7 7 . 9 4 . 3 0.187b 2 . 1 6 1 . 1 1 . 9 9 5 . 0 2 . 7 99.6 8 gas. There are insufficient data here t o 9 21.6 73.8 4.7 0.119 2.25 1.4 1.5 93.8 3.7 99.0 10 13.1 84.1 2.8 0.128 2.01 1.3 1.0 95.5 2.1 98.6 justify any recommendation regarding a 11" 21.9 72.5 5.6 0.109 2.26 1.3 1.4 92.6 4.1 98.0 method for estimating the sulfur distribua Mercaptan sulfur of composite gasoline from riins 5 , 6, and 11 was 0.023. b Appears t o be in error. tion in the gas and bottoms fractions from thermal cracking. n k d e VI.
Yields a n d Product Inspections f r o m T h e r m a l Cracking Wyoming Crude Fractions
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LITERATURE CITED had been analJ7zedby the bomb method, the low eulfur (?Ontent Of the naphtha Rould have necessitated a two- to fourfold difference in the two methods to account for the low recovery; spot sa,mplies indicated this difference t o be only about 10%. The data on sulfur distribution on the stocks from these three orude sources indicate that the sulfur is concentratcd in the bottoms fraction because, in every case, the sulfur content of the
(1) American Gas Inst,., "Gas Chemists' IIandbook," pp. 1613-3, New York, American G a s Inst., 1916. ( 2 ) Egloff,G., Oil Gas J . , 43, No. 7 , 7 4 , 77-8 (1944). (3) I b i d . , No. 14, 76-8. (4) I b i d . , No.28, 218, 221--2. (5) ~ ~M. J.,~and Bent. ~ R .~I)., bid., l 46,~ SO. 28, , 209--15 (1947). R
